Gents I'd like to get your thoughts on a project I have been bouncing around. I'd like to build a studio camera stand to all easier filming and setups in my shop. (2) Vertical C-Beams using XLarge 6 wheel C-Beam Gantry Kit to provide vertical motion for camera arm (shown in blue in attached image) and counterweight (shown in silver) (1) Horizontal C-Beam using XLarge 6 wheel C-Beam Gantry Kit to provide horizontal motion for camera(shown in red) (1) C-Beam Gantry Kit for the mount of the camera on aluminum angle and fluid head Overall it would be approximately 13 lbs of weight on the camera arm with all the components and then a corresponding 13 lbs of counterweight. I've attached rough drawings of what I'm thinking, the trolley / caster platform would have approximately 30 lbs of weight under the platform to give it some heft and keep it planted, I just haven't gotten around to adding this to the Fusion file. I have considered 'boxing' the vertical camera 'tower' C-beam and camera arm with two more XLarge kits using spacers to provide additional rigidity to the system (shown in image), but this seems like a bit overkill, but would like feedback to get everyone's thoughts.
You might get away with hanging a GoPro on the end of this but 13 lbs is not going to happen. You're looking at the strengths of the system and not the main weakness. And that weakness is the 5mm bolt that forms the axle of the wheels. You'll need considerably bigger plates to overcome the amount of leverage you've got on those wheels.
I've thought about a project just like this a lot- tripods, dollied or not, no matter how many things you Magic Arm onto them, are inconvenient to have on the floor unless you have a large building with plenty of floor space between machines/workstations. I want a ceiling-joist-mounted "monorail" system. 20mm rails could probably take the bending moment from the horizontal beam, at the expense of more weight on the vertical beam- not necessarily a bad thing. I don't know that adding rails to the horizontal beam would work too fantastically weight-wise though, that would probably be an opportunity to consider other structures- tube trusses/spaceframe on delrin U-wheels maybe? Something more like a parallel-beam jib crane? I haven't gotten that far yet because something always comes up to kick out the 4x slowdown from camera work into the future, but those are my general thoughts at the minute. I suspect your plans at a counterweighted dolly might run into some issues too- think more along the lines of 150lb of counterweight, not 30lb. That 30lb sitting near the wheels doesn't have anywhere near the leverage your 13lb of camera gear does. Even if it somehow manages to stop the whole thing tipping over, a lightweight system is prone to shake and vibration.
Perhaps, I should clarify a bit.... 13 lbs is ALL the arm weight and the camera weight. Camera, monitor, batteries, etc are less than 5 lbs at the end of the arm. Surely less than 60lb/ft of torque (4 foot arm * 13 lb... which if I calc'd the centroid of mass wouldn't be 4 feet at the end of the arm, because the weight of the arm itself is not applied all at the end) isn't going to sheer one, much less 6 M5 bolts? i mean the shear resistance of a Grade 4.6 M5 bolt is 600+ lbs. I guess I could dust off the old statics and dynamics text books and run the real numbers, but most likely I will just go with the boxed design and see if it breaks.. If it does then it is a only a matter of having longer plates machined and adding more wheels to distribute the forces across more axles. I'll report back with the good or bad news! Thanks for the feedback as it is really appreciated!
5lb doesn't seem like much for a camera rig. C-Beam weighs about 7lb, decent fluid heads about 4lb. 2lb would cover a tiny camera like an A6600 with a kit lens, but no real substantial glass. Then there's still the monitor, mics/receivers/recorders/whatever, batteries, fill lights, SSDs, etc. But if you have the stuff, may as well give it a shot. Wouldn't be the first time instinct lost against testing. That said, I'd still go heavy on a dolly regardless, just for the inertia values. It's not gonna turn your shot to jelly if you brush against the base by accident- aluminum is already prone to vibration conduction, and you're building what's basically a giant tuning fork with plastic hinges. I'd probably put 1" or 2" steel tube down there so I could use standard weight plates, but concrete is always a cheaper option (and is damping, but so is cast iron).
Its a pretty light setup overall... Sony A7C - 509 g Sony FE PZ 16-35mm F4 G - 353 g or Sony FE 35mm f/1.4 524 g iFootage K5 Fluid Head - 760 g Ninja V - 360 g So that is just under 5 lbs... Batteries, etc are external and will be on tower most likely, but even if both the Ninja and A7C have batteries in the (158 g and 86 g respectively) then I'm just over at 5.28 lbs so any other misc items, plus arm hits right at the 13 lbs mark. The base will be CNC'd out of baltic birch (laminated to 2") and the tower supports will be CNC'd out of baltic birch as well (laminated to 1").... But I took your point on putting additional weight in the base so I will add another 30 lb weight plate slung under the base a mere 1" off the floor, so as low a center of gravity as possible. Steel plates are 3 times the weight / in3 as concrete and I'm REALLY tight on space so every little bit counts. And while I understand the point that mass is your friend on stability, I'm not overly concerned with an accidental bump. I'll just cut the shot and start again... Which happens ALOT right now with my current tripod setup and trying to get around it in my tiny shop. But really its now a moot point cause I have placed my order and have all the parts and pieces for the boxed arm and tower design on the way! So crossing fingers that everything works out. Like I said in the opening I am FAR more likely to over-engineer and over-build things than to not, so I'm trying to exercise a bit of restraint on this design. I did look at a number of other builds that I could find with similar setups... Here is a build that uses a large steel center tube as the tower with the counterweight in the middle. The camera arm is longer than what I'm going to be running and the wheels/bearings/plate design for the horizontal arm is not too dissimilar to what I've shown, so here's hoping it works out- But regardless I will update this post as things come together or catastrophically fall apart!
Sorry, had a 12hr shift today so I couldn't get back to this sooner. Let's go through this to come up with something workable. The problem with this point is that all 6 bolts aren't effective. Were it a 6-hole plate bolted to another 6-hole plate, yes all would be effective but you're dealing with wheels here. Envision a gravity load on the 6-wheel pattern (3 top and 3 bottom), the gravity load is merely supported by the lower 3 rollers. It's pulling away from the top rollers so on a simple gravity case they don't enter into the equation. But simple gravity isn't the case here. You've got a torsion load on this plate. In reality only 2 bolts in the pattern have any effect, the lower corner on the camera side and the upper corner on the back side. The four other bolts could be removed from the system with no impact. The beam is pulling away from the opposite corners and the middle bolts are neutral axis bolts with functionally no load. (Yes, the opposing corner bolts will have an impact when the beam is pushed back but we're working through the worst case loading here.) So based on the loads you stated in your second post, and assuming a 5' beam with 8" behind the support and 4" beyond the camera center making a 4' lever arm the total moment applied to the joint will be around 32 foot-pounds. Dividing that by the 4" back span on the bolt spacing that means you've got 96 pounds per bolt. (And yes I understand the lower front bolt will have a slightly larger load due to the gravity load but as I've had a long day, I'm keeping the math simple.) So back to the 96 pound load on the axles. As you state: While this may be true, failure load is irrelevant. Serviceability is what matters. To explain this point, envision the case of a 1500lb pool table on the second floor of a house causing the floor to sag to such an extent the table cannot be leveled sufficiently to where it can be used. All the balls keep rolling to one corner. While the floor hasn't failed, the table is not serviceable. In the case at hand, the 96 pounds may cause the wheels to deflect which in turn will cause the end of the beam to deflect. Even worse, as the axles are dealing with bending of the axles more than shear there may be a slight springiness causing the end to bounce as you move it. So what are the solutions? Honestly, the best solution is a larger plate to where you can get a wider spacing on the wheels thus reducing the load. With a greater spacing you also have the room to add a second wheel just in from the first which also helps further reduce the load on the outer wheel. Another option would be replacing the standard bearings in the main load-bearing corner wheels with 8x16x5 bearings to where you can use an 8mm axle bolt. Ultimately it sounds like you accept there may be some trial and error getting this to work and that is a very good outlook to approach this with. As for the counterbalance, consider a constant force spring instead. Far easier to work with. Just leave the extra weight at the bottom where it does the most good.
Perfectly put- for cameras or CNC machines, it's servicability, not failure. Deflection and deformation are the usual enemies, not outright failure. The torsional deflection is also being multiplied across two sets of wheels- the counterweight may balance the weight of the arm, but it doesn't countervail the twisting of the carriage from the leverage. Stress-wise, you have twice as much plastic in your load path as it initially seems, so as a percentage of deformation, there's also twice as much. Which is why I said vertical rails to begin with. 8mm wheel bearings are also a good call. Anticipating trial and error is almost always a good approach, though. Just maybe not with a $3k rig mounted on the end.
I built this over the past year for stop & live motion and have dealt with plenty of frustrations along the way. I run it with Dragonframe using their DMC-32 for 8 axis's. I have the whole thing torn down right now and rebuilding it to strengthen it all up with larger (wider) plates with more wheels as well as filling the voids to dampen vibrations. Fell free to reach out to me directly to discuss. Its been a real work in progress and I have learned a lot and keep applying it along the way. Here you can see it in action: https://www.instagram.com/p/Cg2OT5KJghc/
